Supports for rotating or oscillating members



May 18, 1965 P. J. GILINSON, JR 3,184,271

SUPPORTS FOR ROTATING OR OSCILLATING MEMBERS Filed May 15, 1957 4Sheets-Sheet 1 Fig. I

Fig.2

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\.l T1 T2 T3 T4 2 v 20' 20 20 Fig.3

CURRENT INVENTOR.

PHILIP J. GILINSON,JR.

mwm, mum WI'I'I'ER & HILDREIH ATTORNEYS May 18, 1965 P. J. GILINSON, JR

SUPPORTS FOR ROTATING OR OSCILLATING MEMBERS Filed May 15, 1957 4Sheets-Sheet 2 Fig. 4

LEAD LAG NET Fig. 5

INVENTOR. PHILIP J. GILINSON,JR.

KENWAY, .ItNNEY, WHTER & HlLDRETH ATTORNEYS y 8, 1965 P. J. GILINSON, JR3,184,271

SUPPORTS FOR ROTATING OR OSCILLATING MEMBERS Filed May 15, 19s": 4Sheets-Sheet :s

1 Fig. 6

H 6 T t 1 4 Fig. 7

INVENTOR.

PHILIP J. GILINSON, JR.

KENWAY, JENNEY. WITIER & HILDREIH ATTORNEYS P. J. GILINSON, JR 3,184,271

SUPPORTS FOR ROTATING 0R OSCILLATING MEMBERS Filed May 15, 1957 May 18,1965 4 Sheets-Sheet 4 7/ Ill/Ill III IN ENTOR. PHILIP' J. GILINSON, JR

KtNWAI, JtNNtY, WITTER & HILDRETH ATTORNEYS United States Patent3,184,21 I SUPPORTS FOR RGTATING 0R OSCILLATHNG MEMBERS Philip J.Gilinson, lax, Chelmsford, Mam, assignor, by

mesne assignments, to Massachusetts Institute of Technology, acorporation of Massachusetts Fiied May 15, 1957, Ser. No. 65%395 '1'Claims. (til. 308-) The present invention relates to supports forrotating or oscillating members and more particularly to magneticbearings for supporting such members without the use of conventionalbearings.

The type of apparatus to which the present invention is especiallysuited is the gyroscopic apparatus described in the Jarosh, Haskell &Donnell Patent No. 2,752,791, dated July 3, 1956, although it may alsobe used for other rotating or oscillating members, particularly Whereprecision of operation and freedom from frictional effects are required.In the Jarosh et a1. patent which will serve as an example forapplicability of the present invention, there is a gyroscopic unit whichis mounted within a cylindrical case, which in turn is floated Within anouter casing. The density of the float liquid is such as to buoy theinner case as freely as possible, and the clearance space between theouter casing and the inner case is preferably very small, of the orderof a few thousandths of an inch. The buoying liquid then acts as adamping medium to damp motions between the inner case and the outercasing. This provides what is termed the integrating gyro. In the formof apparatus shown in the patent the axis of the inner casing is fixedby conventional bearings, and it is one object of the buoying medium toreduce the load on the bearings as much as possible. In someapplications of the gyroscopes where high precision is required, thefriction due to the bearings may still be too high, not withstanding thebuoyancy of the liquid.

It is the object of the present invention to provide a magneticsuspension by which rotating or oscillating member may be magneticallysupported in a precise position without the necessity for use ofconventional bearings.

With this object in view the present invention comprises units of thegeneral type described in the Mueller Patent 2,488,734 (known asmicrosyns), together with external circuit connections arranged toprovide centralizing forces to support the rotating or oscillatingmember. In the several forms of the present invention stator units ofthe type shown in the Mueller patent are used, and in some forms of theinvention the rotor is of circular cylindrical form. This constructionallows the supported member to be either oscillated or rotated.

Another feature of the invention contemplates the use of microsyndevises which are not only capable of performing their signal or torquegenerating functions, but also serve as rotor supports. As described inthe Mueller patent, the rotor and windings of the microsyn may he anranged to form either a signal generator or a torque generaton in thelatter case, the generated torque may either be uniform or may vary withangular displacement. The above Iarosh et a1. patent describes the useof a torque generator at one end of the shaft and a signal generator atthe other end of the shaft. According to the present invention themicrosyn units are arranged to perform their normal functions and stillprovide for the mag netic support of the inner casing.

A further feature of the invention consists of an arrangement forcentering the unit axially.

A further feature of the invention consists of external circuits ofsimple form to provide the necessary electrical currents to the microsynunits for effecting proper support of the supported member. In one formof the invention a simple resonant circuit is used and in another formof the invention feedback circuits are used to give greater stiffness tothe support assembly.

Further features of the invention consist of certain novel features ofconstruction and combinations and arrangements of parts hereinafterdescribed and particularly defined in the claims.

In the accompanying drawings, FIG. 1 is an end View of a magneticbearing according to the present invention;

FIG. 2 is a diagram of connections;

FIG. 3 is a graph illustrating the operation of the apparatus;

FIGS. 4 and 5 are diagrams of feedback circuits;

FIG. 6 is an end view of a modified form of the invention;

FIG. 7 is a diagram of the connections for the apparatus of FIG. 6;

FIG. 8 is a side view of an axial restraint device, and

FIG. 9 is an end view of another modified form of the invention.

In FIG. 1, I show an end view of a magnetic support or hearing device atone end of a shaft which is indicated at 10. Any suitable member whichis not shown may be mounted on the shaft. The magnetic support for theshaft comprises a rotor 12 which is here shown as being cylindrical inform, the rotor being mounted within a microsyn stator 14 of the generaltype described in the above-mentioned Mueller patent. The stator 14-comprises a ring 16 of magnetic material with four salient polesdesignated P to P Each pole has a coil 2b. In the simple connectionsshown in FIGS. 1 and 2 one end of each of the four coils is grounded andthe other is brought out to a suitable terminal. The four terminals aredesignated at T to T As shown in FIG. 2 each of the coils is externallyconnected in series with a condenser C, and the four condenser-coilcombinations are connected in parallel to a suitable source ofalternating current indicated at V.

The coils are preferably energized to produce alternately inward andoutward instantaneous fluxes in consecutive poles.

The forces acting to support the rotor 12 can best be explained byconsidering the two opposed poles P and P lying along the axis X and thetwo opposed poles P and P lying along the axis Y. If the rotor isexactly centered, there is no net magnetic force tending to move therotor in any direction. The circuit parameters are such that any slightdisplacement of the rotor away from its center position results in a netmagnetic force which restores it to its center position.

Considering first the two poles lying along the X-axis, let it beassumed that the rotor is displaced a small distance x toward theright-hand pole face, thus diminishing the right-hand air gap andincreasing the left-hand air gap. The inductance of the right-hand coilis increased and that of the left-hand coil is reduced. The seriescondenser C is of such magnitude that the operating point of each RLCcircuit of FIG. 2 is on the down slope of the resonance curve, so thatan increase of inductance of any coil results in a decrease of currentin that coil. A plot of current against inductance is given in FIG. 3.When the rotor is centered the inductance of any coil has the value LThe quiescent current is I Upon a displacement to the right theinductance of the coil on P increases to L and hence the current isreduced, while the inductance of the coil on P decreases to L and thecurrent in the coil increases.

The magnetic energy in the air gap due to any coil is LI and themagnetic force acting on the rotor due to that coil is the derivative ofenergy with respect to displacement. The changes in the inductances ofthe two coils upon the ocurrence of a small displacement, x, may becalculated from the changes in reluctances of the air gaps, and thechanges in currents in the coils may be calculated from the changes inthe inductances, so that an analytic determination of the resultantforce may he obtained. It may be stated in general that the componentsof force due to inductance changes alone are non-centralizing (i.e., aslight motion away from center would result in continued motion untilthe rotor contacted one of the pole pieces), but the components of forcedue to changes of current are centralizing, and they overbalance thenon-centralizing components. Stated in another way, the center positionis a position of minimum energy, and the axis is centralized by virtueof the tendency of the system to assume the minimum-energy condition.

The same considerations apply to the poles P and P on the Y-axis. Hencethey apply to any components of displacement along the X- and Y-axes andtherefore to a displacement in any direction; in other words, any slightdisplacement from the symmetrical center position results in a forcewhich restores the rotor to center. Hence the magnetic suspension actsas a bearing to fix the shaft, without, however, introducing anyfriction of the type encountered in conventional metal-to-metalbearings.

The magnitude of the centralizing force depends on the size of themicrosyn, the magnitude of the quiescent current, the circuit parametersand also upon the frequency.

The suspension may be stiffened by the use of a feedback circuit. Twotypes of feedback circuits are shown in FIGS. 4 and 5. In FIG. 4 thereis what is termed an alternating current feedback circuit. The X-axiscoils 24) are connected in series with the condensers C to inputresistors R to the junction of which is connected the source V. Atransformer 21 has its primary connected across the resistors, and itssecondary connected through a divider network 22 to the grids of a dualtube 24, the plates of which are connected to the terminals T and T ofthe coils. A substantially identical circuit is provided for the Y-axiscoils. An increase in the magnitude of the current in one coil isacompanied by a decrease in the magnitude of the current in the othercoil. The signals from 22 as impressed on the tube 24 are used to feedpower to the coils 20 in such directions as to cause centralization ofthe rotor. Some centralizing effeet is obtained from the resonancecondition existing as shown in FIG. 3 and the centralizing force due tothis condition is enhanced by the amplified power fed back to the coils.As heretofore noted, the centralizing forces are those due to thechanges of current, whereby the decentralizing forces due to inductancechanges are overbalanced; the feedback circuits amplify the currentchanges and hence increase the centralizing forces.

The purpose of the divider networks is to permit the initial setting tobe made for precise centralization without unbalance torques.

Another form of network is shown in FIG. in which direct current poweris fed to the coils. This is shown for the Y-c0ils only, and a similarnetwork will be duplicated for the X-coils. The coils iii are excitedfrom alternating current through the condensers C as in FIG. 1. Acrossboth coils in series is the primary of a signal transformer 26, thesecondary of which feeds into a preamplifier 28 and a demodulator 39.Any shift of the rotor will result in such changes of impedance in theseries circuit of the two coils as to cause a change of voltage acrossthe coils. Hence the output of the demodulator Stl comprises afluctuating direct current the magnitude of which is dependent on thedisplacement of the rotor from its symmetrical center position. Theoutput of the demodulator is fed into a lead-lag network 32 and hence tothe grids of tubes 34, the outputs of which are applied to the coilsZtl. This gives a stiff suspension by which the centralizing force dueto the resonant condition is materially enhanced. The lead-lag networkmay be of a type familiar in the servo art. In general, a lead networkis a high-pass filter while a lag network (or integrating circuit) is alow-pass filter. The lead-lag network 32 therefore emphasizes the highand low frequencies. The high frequencies improve the stability of thesystem and increase the centralizing forces, while the integration dueto passage of low frequencies tends to eliminate long-term err rs.

In any of the systems thus far described there will be some tendencytoward radial oscillation. The rotor and shaft will tend to oscillate ata frequency determined by the mass of the suspended elements and thestiffness due to the magnetic centralizing forces. It is desirable thatthe radial motions be damped. Therefore the invention is particularlyuseful in connection with floated damped instruments of the typedescribed in the abovementioned iarosh et 211. patent since the dampingfluid itself will serve to damp any radial oscillations.

The apparatus shown in FIG. 1 may be used either for an oscillatingshaft or a rotary unit. Since the rotor 12 is cylindrical it may be usedwith a continuously rotating shaft.

The preferred forms of the present invention reside in the use ofmicrosyn units which are constructed to perform their regular functionsand also to serve as a magnetic hearing or suspension. From the Muellerpatent above-mentioned it will be clear that the microsyn unit as usedfor uniform-torque or signal generation requires a minimum of four polesin order to maintain total fluxes constant upon rotation of the rotor.According to the present invention a minimum of eight poles is requiredin order to maintain total fluxes due to the rotation of the rotorconstant. The preferred form of microsyn is shown in FIG. 6. The rotor35 has four protruding pole faces 36. The stator 37 is provided witheight reentrant poles 33 which are numbered from 1 to 8 in the drawing.Each pole face 36 of the rotor spans the distance between centers ofadjacent stator poles. In FIG. 6 the primary windings 39 are fully shownon the poles. Each pole has a secondary winding 39, shown on one of thepoles only. The windings are so arranged that with the rotor in itsnormal zero position, the instantaneous fluxes are in one direction inpoles 1, 2, 5 and s and in the opposite direction in poles 3, 4, 7 and8. They are shown as ingoing fluxes in poles 1, 2, S and 6 and outgoingfluxes in the other poles. (The showing of the windings themselves inFIG. 6 is conventional, and no effort is made to indicate windingdirections or numbers of turns; the primary windings are arranged toproduce the relative flux directions indicated by the arrows, and thesecondary windings are connected for either torque or signal generationin accordance with the teachings of the Mueller patent.)

A schematic view of connections is given in FIG. 7. The primary windingsare numbered 1 to 8, and each secondary winding 39 is adjacent to itscorresponding primary winding. The primary windings are connected inseries pairs with the terminals T to T., as in FIG. 2, and each pair isconnected in series with a condenser C. The four coil-condenser seriescircuits are connected in parallel with each other and to a voltagesource V.

The secondary windings are all shown as connected in series.

It is necessary to consider both rotational and radial displacements ofthe rotor.

First, with respect to rotation, it will be observed that if the rotorturns, say, through a slight angle in a clockwise direction thereluctances of the air gaps 1 and S will increase while the reluctancesof air gaps t and 8 will decrease, so that the total inflowing flux willremain constant. The outflowing fluxes in poles 3, 4, 7 and 8 will alsoremain constant. Thus the conditions for uniform total flux in thetorque generator or signal generator shown in FEGS. 2, 3 and 5 of theabove-mentioned Mueller patent are satisfied, the only difference beingthat each of the four poles of the Mueller patent may be considered tobe divided into two poles. The secondary may be energized from itsterminal to generate a torque, or an outputsignal may be taken from thesecondary.

In order to examine the conditions existing upon a radial displacementlet it be assumed that the rotor is displaced from its center positionslightly along the X-axis which is here shown as lying symmetricallybetween the centers of poles 1 and 8. The air gaps at 1 and 8 will thendecrease and the gaps at poles 4 and 5 will increase. Each such pair ofprimary coils is connected in series with a condenser C as shown in FIG.7. By proper choice of the size of the condenser so that operationoccurs on the down slope of the resonance curve, the currents in thecoils on 4 and 5 can be made to increase and those in the coils on 1 and8 to decrease in a manner to provide a centralizing force along theX-axis in exactly the same manner as in FIG. 1. Likewise, any motion ina radial direction along the Y-axis will produce a centralizing force.

From the description thus far given it will be seen that the actions ofthe microsyn of FIG. 6 in respect to rotation and radial displacementare completely independent and uncoupled. In other words, a rotationalmovement of the rotor generates either a torque or signal in exactly thesame manner as described in the Mueller patent, while a radial motionproduces a centralizing restoring force to maintain the shaft in theproper position. Hence the microsyn serves as both a torque or signalgenerator and a centralizing device.

When greater radial stiffness is desired, the feedback circuit of eitherFIG. 4 or FIG. 5 may be used. It is only necessary to connect theterminals T to T to the correspondingly designated terminals of FIG. 4or 5. The feedback circuits operate in the same manner as previouslydescribed to provide large centralizing forces against radialdisplacements, while leaving the microsyn free to respond in its usualmanner to rotational displacements.

in the use of gyroscopic instruments of the type shown in the larosh eta1. patent, a torque generator is frequently used at one end of theshaft and a signal generator at the other end. According to the presentinvention, the torque and signal generators may be arranged to serve asmagnetic bearings to support the inner casing. They may also be used toprovide axial restraint, so that conventional thrust bearings may bedispensed with.

FIG. 8 shows the means of providing axial restraint. A floatedinstrument 40 may be the inner case of the gyroscopic instrument of thelarosh et al. patent. The floated instrument is contained within acasing 42, there being a slight clearance space between the parts 4t)and 42 which is filled with a viscous floating and damping liquid 44 asdescribed in the larosh et a1. patent. At each end of the shaft 46 is amicrosyn rotor, the two rotors being indicated at 50 and 52, each rotorbeing centered within a stator indicated diagrammatically at 54 and 56.The rotors may be circular in end view, as in FIG. 1, or may be providedwith poles, depending on whether rotational sensitivity is desired. Asshown in FIG. 8 the pole faces of the rotors 5d and 52 of the stators 5dand 56 are tapered in opposite directions. Each stator pole is providedwith a suitable winding or windings, indicated at 58. The severalwindings may be connected into any one of the external circuits shown inFIGS. 2, 3, 4 and 7. The conditions that provide radial centralizationalso provide axial restraint since if there is any tendency for the unitto move to the right or left, the air gap in one of the units willincrease and that in the other will decrease, thus bringing about achange of currents to restore the proper axial position.

As heretofore noted, it is desirable in operation of this system thatradial damping be applied in order to minimize oscillatory effects. Thisis provided by the gyroscopic member itself as described in the Jaroshet al.

6 patent. Such damping also damps any axial movements in FIG. 8.

The forms of microsyns heretofore described are signal generators oruniform-torque generators, comprising some of the types described in theMueller patent. Also described in the Mueller patent is an elasticrestraint generator, which is a generator capable of generating a torquethat increases with angular displacement from a neutral position. Thisgives the effect of a torsional spring. In this case a secondary windingis not necessary and it is only required that each primary winding beconnected in series with the condenser, the several coil-condensercircuits being connected in parallel. The coils are connected so thatinfiowing and outflowing fluxes alternate. In such a system the totalinflowing or outflowing flux is not a constant independent of rotorangular displacement, but actually varies as the rotor is displaced.Hence, for a magnetic suspension involving an elastic restraintgenerator it is only necessary that four poles be used as shown in FIG.9, although any multiple of four poles may also be used. The windingsare connected to give the instantaneous fiux pattern shown in FIG. 9,which is the same as in FIG. 3 of the Mueller patent. This is to bedistinguished from the signal generator or torque generator in whichsome multiple of four poles, not less than eight, is required.

The windings of FIG. 9 are preferably externally connected in exactlythe same fashion as in FIG. 1 whereby rotational, radial (and axial)centralization may be attained.

Having thus described my invention, I claim:

1. Microsyn apparatus comprising a stator having a multiple of fourpairs of poles, a rotor having circular arcs equal in number to thepairs of poles, each arc spanning adjacent poles, primary coils on thepoles arranged to direct fluxes inward and outward in the poles of eachpair, a plurality of condensers to form with the primary coils a numberof resonant circuits, means for energizing said circuits so that therate of change of current in any coil with respect to the inductance ofthe coil is negative, whereby radial centralizing forces on the rotorare generated upon any departure of the rotor from a centralizedposition, and secondary coils on the poles to carry microsyn currentsrelated to the angular position of the rotor.

2. Microsyn apparatus comprising a stator having a multiple of fourpairs of poles, the poles of each pair being adjacent, a rotor havingcircular arcs equal in number to the pairs of poles, said arcs spanningpoles of adjacent pairs, primary coils on the poles, the coils of eachpair being connected to direct fluxes alternately inward and outward inthe coils of each pair and to direct fluxes in the same direction inadjacent poles of adjacent pairs, a condenser connected with each pairof primary coils to form a resonant circuit, means for energizing eachresonant circuit at such a frequency that the rate of change of currentin any coil with respect to the inductance of the coil is negative,whereby radial centralizing forces on the rotor are generated upon anydeparture of the rotor from a centralized position, and secondary coilson the poles to carry microsyn currents related to the angular positionof the rotor.

3. Apparatus according to claim 2 having means to measure differences involtages across opposed pairs of coils and amplifier means to vary thecurrents in the coils to increase the radialcentralizing forces on therotor.

4. A gyroscopic unit comprising an outer casing, an inner casing havinga shaft, a buoying liquid within the outer casing to float the innercasing, and two microsyn devices as claimed in claim 2, each having arotor on the shaft, the liquid acting to damp both rotational and radialmotions of the inner casing.

5. An elastic restraint generator comprising a stator having foursalient poles, a rotor having two circular arcs spanning adjacent poles,coils on the poles to direct fluxes alternately outwardly and inwardly,a condenser in series with each Winding to form a resonant circuit, andmeans for energizing the resonant circuits such that the rate of changeof current with respect to inductance is negative, whereby radialcentralizing forces on the rotor are generated upon any departure of therotor from a centralized position and whereby, upon angular displacementfrom a neutral position, a torque increasing with said displacement isgenerated.

6. A magnetic bearing comprising a stator having a number of salientpoles, a rotor of magnetic material, a coil Wound on each pole, acondenser in series with each coil and forming a resonant circuit, meansfor energizing the resonant circuits so that the inductive reactance ofeach coil is slightly greater than the capacitive reactance of itsassociated condenser, whereby each resonant circuit is energized at asteep portion of the resonance curve wherein the rate of change ofcurrent with respect to inductance is negative, to provide radialcentralizing forces on the rotor, means to measure voltages across thecoils, and amplifier means for varying the currents in the coils toincrease the radial centralizing forces on the rotor.

7. Apparatus according to claim 6 in which the coils are connected inpairs according to coordinates, measuring means for comparing thevoltages across the coils of the separate coordinates, and amplifiermeans for varying the currents in the coils in a direction to increasethe centralizing forces on the rotor.

References Cited by the Examiner UNITED STATES PATENTS 1,589,039 6/26Anschutz-Kaempfi 308-10 2,377,175 5/45 Peer 30810 2,602,660 7/52 Shannon308-10 2,733,857 2/56 Beams SOS-10 2,809,526 10/57 Lundberg 308-10MILTON O. HIRSHFIELD, Primary Examiner.

ORIS L. RADER, NORMAN H. EVANS, Examiners.

1. MICROSYN APPARATUS COMPRISING A STATOR HAVING A MULTIPLE OF FOURPAIRS OF POLES, A ROTOR HAVING CIRCULAR ARC EQUAL IN NUMBER TO THE PAIRSOF POLES, EACH ARC SPANNING ADJACENT POLES, PRIMARY COILS ON THE POLESARRANGED TO DIRECT FLUXED INWARD AND OUTWARD IN THE POLES OF EACH PAIR,A PLURALITY OF CONDENSERS TO FORM WITH THE PRIMARY COILS A NUMBER OFRESONANT CIRCUITS, MANS FOR ENERGIZING SAID CIRCUITS SO THAT THE RATE OFCHANGE OF CURRENT IN ANY COIL WITH RESPECT TO THE INDUCTANCE OF THE COILIS NEGATIVE, WHEREBY RAIDAL CENTRALIZING FORCES ON THE ROTOR AREGENERATED UPON ANY DEPARTURE OF THE ROTOR FROM A CENTRALIZED POSITION,AND SECONDARY COIL ON THE POLES TO CARRY MICROSYN CURRENTS RELATED TOTHE ANGULAR POSITION OF THE ROTOR.